Asteroid Mining: A Marker for SETI?

byPaul GilsteronMarch 29, 2011

Having just finished Iain Banks’ The Player of Games, I’m thinking about the ‘orbitals’ he describes in his series of novels about the Culture, a vast, star-crossing civilization that can build space habitats in the form of massive rings. Orbitals are smaller than the kind of ‘ringworld’ Larry Niven envisioned, but huge nonetheless, bracelets of super-strong materials housing billions who live on their inner surfaces as they orbit a parent star. The visual effects Banks pulls off in describing these habitats are spectacular. And now a new paper by Duncan Forgan (University of Edinburgh) and Martin Elvis (Harvard Smithsonian Center for Astrophysics) has me wondering about the kind of mining activities it would take to produce the raw materials for such constructs.

Forgan and Elvis are interested in what they describe as a multi-wavelength, multi-signal approach to SETI. We’re used to the idea of huge radio dishes listening for extraterrestrial signals, but SETI is evolving through the use of optical methods, and moving in another tangent into ways of searching for extraterrestrial artifacts on the grand scale, like Dyson spheres. Throw in our ongoing hunt for terrestrial-class exoplanets through missions like Kepler and you have a broadly based strategy open to the detection of another civilization. The authors’ new paper suggests adding one more place to look: In the debris disks around other stars, where we might find signs of asteroid mining for raw material.

Image: Iain Banks’ Consider Phlebas has appeared with a number of different covers, but this one gives you a sense of the scope of the ‘orbitals’ he writes about, vast technological ‘bracelets’ on which billions live. What would it take to produce the raw materials for an orbital? Would we be able to detect such work as it progressed?

Data Mining in a Debris Disk

Debris disks are what’s left over when the gaseous disks around young stars go through their normal evolution, leaving rocky and icy debris in various sizes, like the comets and asteroids found in our own Solar System. We’ve been learning a great deal about debris disks through spectroscopy and imaging ever since the first detection of such a disk around the star Vega, back in the 1980s. These days, we have finely tuned instruments like the Herschel Space Telescope and Spitzer that can provide a wealth of new data. How could we use that data to search for potential evidence of an extraterrestrial intelligence manipulating a debris disk?

It’s a fascinating notion (and thanks to Adam Crowl for calling my attention to this paper). The authors assume that the engineering limitations we have experienced in our own history will also hold for alien cultures. Like us, they will need large quantities of raw material to build the structures their civilization requires. And like us, if we are ever to build a spacefaring civilization, they will need to mine such materials as they move into nearby space, building space vehicles and large habitats as sections of the population move off-planet. Both biological and post-biological civilizations will, then, need the resources demanded by their own growth.

From our perspective, targeted asteroid mining (TAM) presents high initial costs but great potential for profits, lowering the costs of manufacturing future technologies. In fact, Forgan and Elvis argue that the expertise we would gain by creating the necessary infrastructure for asteroid mining could be brought to bear on other aspects of space exploration. Given its hazards, asteroid mining is likely to be turned over quickly to automated workers, putting an emphasis on developing advanced artificial intelligence as we evolve a post-biological culture.

From the paper:

ETIs which have similar economic concerns to ours will eventually find extraplanetary mining projects desirable as their own resources become depleted (provided of course they are sufficiently technologically advanced). We suggest the complexity of TAM missions are such that most species capable of it have the potential to become truly space-faring. If technological civilisations more advanced than ours exist in the Galaxy, a distinct possibility given the estimated median age of terrestrial planets being around 1 Gyr older than Earth (Lineweaver, 2001), and asteroid mining is a common activity which underpins their existence, then searching for signatures of TAM is an appropriate activity for SETI to undertake.

The Signature of Targeted Mining

All of which leads us to the kind of artificial observational signals we might hope to detect. The paper studies this question in relation to the Vega debris disk and finds three kinds of disequilibrium that might be created by asteroid mining at a large scale. The extraction of specific minerals and elements will create an imbalance in the disk, and the authors note the likelihood of iron and nickel mining, these being of practical use in large-scale space engineering projects, along with rarer elements such as platinum and palladium, useful in technological innovation. A sharp depletion in several of these species would be a potential marker.

So, too, would large-scale mining’s effects on the dynamics of a debris disk system, for we would expect these activities to result in the destruction of the larger asteroids in the system. Unusual temperature distributions are a third possible marker, created by the production of dust in the mining process. An anomalous dust source or an unusual temperature gradient in the disk would provide a potentially detectable signal. For that matter, variability in the disk as different locations are mined could also be detectable, although here we’re talking about future instrumentation, as what we have today probably isn’t sensitive enough to make such observations.

Potential for a Detection

Asteroid mining would be no easy catch. In fact, it’s best seen as part of a larger strategy, and may help us primarily in calling our attention to systems that demand further investigation. Having analyzed the signature from the various mining activities, the authors add:

The general trend is somewhat disappointing. For TAM to be detectable, it must be prolific and industrial-scale, producing a large amount of debris and disrupting the system significantly to be detected. However, instrumentation is continually improving, and sensitivity to such effects will only grow, reducing the constraints on detectability. What remains indefatigable with technological advance is the confusion of apparent TAM signals with natural phenomena. A detection of any one of these TAM signals can be explained with a simpler natural model, but detection of many (or all) of these signals in tandem will prove more difficult to model, and hence TAM more difficult to discount as a possibility.

So targeted asteroid mining appears unlikely to provide us with a conclusive detection of an extraterrestrial civilization, but tentative signals seen in unusual dust size distributions or deficits in chemical composition could be markers that tell us to look at a system more closely. Usefully, the markers of asteroid mining would, unlike biomarkers in an atmosphere, indicate not just life but an intelligent, technology-driven culture. For that reason, the authors argue that searching for asteroid mining signatures is a useful addition to the multi-wavelength, multi-signal SETI strategy that is now evolving as we extend our hunt far beyond conventional methods.

The paper is Forgan and Elvis, “Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence,” accepted for publication in the International Journal of Astrobiology (preprint). And if you’re not familiar with Iain Banks, do look into his novels about the Culture. His plots are ingenious, but I continue to marvel at his visual sense, and always take away images of places that are both astounding and inspiring. Oh to see technology used like this!

I would think if a civilisation were mining their asteroid belt one thing to look for would be drive by-products.
Would the “twinkle” of fusion drives be visible?
If a star system was observed to have a “point” sources of heat, that would be an indication that someone is tooling around in a fusion powered mining ship.

just out of curiosity, how many here think SETI realistically has a chance of finding anything? i’m of the opinion that our best options lie in better and better telescopes searching for exoplanets and sending out more probes in this system (at least until we can get fast enough to go further) and look for microbes on mars, etc.

I disagree that asteroid mining should a priori result in destruction of the largest asteroids in a population. It may be far more efficient, say, for a processor to ‘consume’ asteroids of a particular arbitrary size, and not deal with the largest rocks due to the requirement for techniques more similar to surface mining.

On the other hand, the requirement to move a processor from small target to small target obviously introduces another inefficiency, so I suppose that rather than fixating on a particular size band for any observable signal in asteroid populations, it’s more prudent to simply remain agnostic.

There are an awful lot of logical leaps about how asteroid mining would be done in this proposal, even before considering whether technological civilizations would use this approach. If advanced civilizations have transcended biological bodies, then we might ask whether they have achieved star flight and mined other systems, including our own? Should we be looking for evidence in our own backyard, even as a validation test?

It makes sense that a civilization would consume its asteroids as it expands into its solar system. However, I think detection of this process would be difficult. First, the largest structures that can be manufacturing, using carbon nanotubes, are about the size of a Bishop ring with a rotational radius of 1000 km. Detection of Bishop rings down to O’neill style habitats from asteroid debris would be very difficult even for space-based telescopes. A Dyson ring of such habitats would appear little different from a natural asteroid belt to a telescope in our solar system.

Banks orbitals require a material with a tensile strength comparable to the nuclear force in atomic nuclei. I doubt such material is possible.

@ Alex Tolley – Probably always prudent to examine our own backyard continually, especially as our understanding of what to look for continues to change. The case has been made by many that possibly objects such as what we classify as viruses may include artifacts of ETI within their population.

I agree strongly with your cautionary tone about preconceptions, but I would argue that exploitation of asteroids seems particularly appealing as a characteristic of any spacefaring ETI, a supposition purely based on the availability of resources. And you’ll mine your own system before any others – again, on principles of access and general laziness.

To answer “the other adam”, I am comfortable with the proposition that no spacefaring species has yet evolved in our Galaxy, and if we continue to progress we will be the first. Remember that the universe is still young: only 13 bn years into a lifetime (measured by the longevity of cool stars) of over a trillion years. But I’m also happy people are looking: I don’t think they’ll find anybody out there, but I’d be delighted to be proven wrong!

So to my mind asteroid mining is more a pointer to where we should be going than something we will find other civilisations are doing already. Obviously, any anomalous observations of stellar dust disks and asteroid belts will attract attention, regardless of whether one is deliberately looking for ETI or not.

(I have a commentary “The strategic role of asteroid mining” in the current, April 2011, issue of Spaceflight, published by the British Interplanetary Society.)

Thanks for the book recommendation; I’ve not yet tried Iain Banks, but will remedy this soon!

Consider how long any such civilizations have likely been around. We’re talking about millions of years. In that time, they are quite likely to have not just consumed asteroids, but all the small bodies of their system, and probably dismantled their planets too. That would seem to imply different “signatures”, if correct. Indeed, I would expect stellar level engineering in that time. As Dyson once suggested, don’t look for microbes on Europa, look for a “fish”. If stellar engineering is out there, we clearly don’t recognize it.

The current search for life, any sort, makes sense to me. Unfortunately, the assumptions about life are very narrow, and worse, very centered on life in the photic zones of earth. It wouldn’t surprise me if we discovered that life could take on many more chemistries (and physics?) than exist on earth. I remember reading Fred Hoyle’s ideas on life in the galaxy and his supposition that he had found a chlorophyll signature. Earth-like chlorophyll? It would be very interesting if we found out that life can/does independently find the same basic biochemistries, much like eyes seem to independently evolve on earth, albeit very differently.

Hi All
Zodiacal dust is thrown off asteroids and comets and is the most visible sign of asteroids and comets in exosolar systems because the effective area is so much larger. How would mining affect the dust? Assuming “messy” mining and there might be more of it, but it might be more spread out. Alternatively the dust might be gathered and shepherded, appearing as regular patterns to outside observers.

The asteroids are too spread out, far more than people know. If I were an alien, I’d be tapping the ice rings of Saturn. Because if I were an alien, I’d probably have enough metals just to get to our solar system in the first place.

I coincidentally stumbled across this paper on astro-ph about 20 minutes before I saw Paul’s post, so I’m really glad that he chose to write about it!

There were two things about the paper that really got me thinking. One is that the paper is focused on asteroid belts that are in the process of being mined. But what would an asteroid belt that has already been thoroughly mined and consequently discarded, look like? Maybe we could look for anomalously depleted asteroid belts for signs that an industrial civilisation has been there. But to identify a belt depleted by mining we need to better understand the characteristics of debris discs around all kinds of stars. For instance, evidence for an asteroid belt 25 times more massive than our own, seen by Spitzer around the star HD 69830, was found in 2005; it makes our own belt look depleted by comparison. So it suggests we have a lot to learn about asteroid belts and debris discs before we can say we know how to recognise the signs of mining.

The second thing that got me thinking was a brief discussion early in the paper about the costs of any future mining of our own asteroid belt. They quote other authors who have optimistically estimated minimum costs of at least $15 billion for a commercial asteroid mining enterprise, and that is based on technologies we don’t yet have, such as nuclear fusion using helium-3 mined from the Moon. But they also state that as certain resources begin to run dry on Earth, more money, research and development will be put into asteroid mining missions. I have to seriously question this. Now is the time to start looking to the asteroids, not in 50 or a 100 years when we are beginning to run low on some resources, because by then we may not be able to gather the investment and resources necessary to fund such a mission when faced with combating climate change, overpopulation and depleted resources. The idea that a near Earth asteroid may be the next stop for manned spaceflight within the next decade gives me some hope, but with all the best intentions in the world we know that such a mission is hardly guaranteed to happen and, even if it does go ahead, how long will it take for private enterprise to catch up? After all, private flights are only just beginning to get to grips with sub-orbital manned flight. Maybe I’m just being pessimistic?

On the other hand, if concerns about METI are justified and aliens really do invade, they’re more than likely to invade the asteroid belt than Earth! There was a terrific Stephen Baxter book called ‘Space’ that featured a similar scenario.

We would go for the asteroid belt first, then the gas giant moons later as the technology developed. The gas giants themselves would eventually be mined for volatiles. Perhaps we should be looking for “depleted” gas giant plants, if we know what one would look like.

The distribution of elements will vary as one moves away from the central star. The closer in bodies seem to have a higher concentration of heavy elements. The outer bodies seem to have lighter element “volatiles”. Lots of solar system resources would be utilized over a billion years.

Some mention PGM’s (Platinum Group Metals). However, the replacements for PGM catalysts may have been developed in the form of polymer dipped carbon nanotubes:

Perhaps advanced civilizations find more and more ways to replace heavy and other metals with light elements, given the comparative abundance of the latter. This would favor utilization of gas and ice planets along with the outer (Kuiper rather than asteroid) belts. In the same way, He3 fusion power gives way to straight D-D fusion, with the resulting neutrons being utilized in some manner (waste not, want not, right?).

Alex Tolley, Hoyle was only referring someone else’s ignored discovery of spectral evidence for interstellar chlorophyll (I can not remember who), but I also found those implications fascinating. How could this be a real detection even under Hoyle’s version of panspermia?

Given that uv degradation would render direct usage implausible, the only way I can think of was also mentioned by Hoyle on a separate occasion. It speculates that the T–Tauri stage of planetary development briefly melts most of its comets, and this is where the business happens. I’m not even sure that such a powerful T-Tauri stage is common enough to drive this mechanism, but when such speculation rests on such fine and testable details it surely becomes even more interesting.

Another great article, thank you! I’ve been wondering for a while, how can we detect a Dyson sphere if it completely incloses the parent star?
Looking forward to reading this series by Iain Banks. Which one do I start with?

Mining asteroids will probably be done in zero-g. It would be uneconomical to move the materials in and out of gravity wells. Likewise, waiting until full blown artificial gravity habitats are constructed will be time and cost prohibitive. This will result in a lot of pressure to evolve zero-g cultures. It is highly unlikely that these cultures will devote generations to building habitats for gravity dwellers such as ring worlds. Moving in and out of gravity wells is grossly inefficient. I think zero-g people rule space. We should be looking for them.

We should keep in mind that the most likely way of “mining” asteroids is not going to be carrying them off never to be seen again. The mass is not going to disappear. More and more asteroids are going to be gone, but in their place there will be whatever the material was used to build. Could we reliably distinguish a belt of asteroids from a belt of habitats? Perhaps habitats will tend to be relocated to the HZ, so an unusual concentration of “debris” in the HZ would be a detectable clue, I suppose. We should observe a preponderance of room temperature objects in the IR spectrum emanating from the disk, for example. Also, habitats are likely to be less dense than the original asteroids, which should increase the apparent density of the belt.

As observed previously by kurt9, Banks orbitals cannot be made from any materials, certainly not those mined from asteroids. The size limit for a structure with full artificial gravity is a few thousand km, due to fundamental tensile strength limitations. These would have to be O’Neill style habitats, with an enclosed atmosphere.

Some stars have unusual abundances of various elements. I wonder if that could be the result of technological activity. Maybe they’ve been siphoning off the other elements, leaving a proportionately larger amount of some elements behind. They find some elements more useful than others…?

Or maybe advanced ETI are using their suns as waste dumps. Some SETI advocates have said for decades that we should monitor stars for any unusual elements that might not normally be part of their makeup.

Some have even argued that ETI could deliberately put certain elements into their stars to get the attention of any astronomers who know how to do spectroscopy.

Just as our first detection of an alien civilization may be their random transmissions or radar beams that were not meant for anyone anyone outside themselves, we may also recognize them by their celestial waste products before anything deliberate and formal comes along. Once again SETI needs to expand its search parameters.

Mark Presco’s remarks about the utility of zero-g cultures certainly makes sense to me. There’s one artifact of solar system engineering that I can think of that might be much more easily detectable than asteroid mining, though keeping that in mind is certainly a fine idea. That idea is large solar energy collectors in close orbits around their stars. Since Kepler has already detected at least one Mars sized object, detecting REALLY large artificial power-sats is ALMOST doable NOW. Since these would naturally NOT be 1-g habitats like Banks “orbitals”, they could actually be quite easily detectable by a “super-Kepler” mission. Where to look? Close in, of course, probably near the orbital radii of hot Jupiters at around 0.05 to 0.10 AU, which naturally leads to orbital periods of around 4-11 days or so. They wouldn’t have to be totally opaque to be detectable but they would likely all be in or near the same orbit with the same orbital inclination. The signal would just be multiple transits, which could mimic much shorter orbital periods, but those could be ruled out on dynamical grounds. The masses of the individual power-sats would be low enough that gravitational interactions between them would be ignorable (but not solar radiation pressure, of course). The photometric signal should really be easily distinguished from transiting planets or starspots. Presumably such energy collectors would then radiate their “catch” to other parts of the solar system (thru microwaves or lasers perhaps), such as the habitable zone. If anyone is interested in working up a serious paper on this (I’m NOT, without collaborators to share the load), I’m sure Paul can figure out a way to put us in contact. We can already just about put some limits on some such systems by using Kepler data. (this is such an obvious idea that it likely has already been thought of, but since I have not run across it (or yet done a search), I thought it might be worth mentioning).

Coolstar, couldn’t this method of detection still be used if there was just one collector? Luc Arnold has pointed out that if a type II civilisation really wants to be detected it could deliberately make artificial close-in eclipsing objects that were decidedly noncircular. Wouldn’t the cost of departure from circularity for a solar collector be so minimal as to act as a far more cost effective METI than Benford Beacons? Perhaps then you could look at larger single candidate planets.

Abstract: The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1 – 4 AU from the star. We find one significant detection (eta Crv), two marginal detections (gamma Oph and alpha Aql), and 22 clear non-detections.

Using a model of our own Solar System’s zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are eta Crv (1250 +/- 260), gamma Oph (200 +/- 80) and alpha Aql (600 +/- 200), where the uncertainties are 1-sigma. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1-sigma). These measurements represent the best limits to date on exozodi levels for a sample of nearby main sequence stars.

A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding eta Crv and gamma Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3-sigma upper-limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.

@Rob Henry I don’t think I’d seen the suggestion by Luc Arnold (or had completely forgotten about it if I had), thanks. Do you happen to have a reference for that? Offhand, it just seems easier (and cheaper) to build multiple things in the same orbit. Detecting that a single object of a given size is non-circular is I think a lot harder than discovering even two transits with the same period, but with the time between them much less than the orbital period.
Once you have the required photometric precision to detect a given area, the precision needed to detect departures from circularity seems roughly about an order of magnitude harder. Such a system (multiple transits with the same period) can’t exist naturally, unless there are quickly observable period changes from dynamical interactions (like horseshoe orbits, for example!). While I’m assuming that power-sats would have to have station keeping thrusters.
A civilization could even communicate using this idea (with very low bandwidth!) by systematically varying the separation between the satellites in non-natural ways. Interstellar semaphore!

Coolstar, I love the allusion of stage II civilisations sending out ‘smoke signals’. I think that if we do ever find an intention message, its method of transmission will have some equivalently unexpected aspects to it.

Finding a near-Earth asteroid worth landing on is harder than it seems, say rocket scientists.

kfc 05/24/2011

What next for the human exploration of space? One idea is to send the next generation of astronauts to explore a near Earth asteroid.

Let’s set aside, for a moment, the question of whether human exploration of space is viable and look at the supposed benefits of visiting a passing rock.

First, asteroids are of enormous scientific interest, being remnants of the primordial Solar System. Second, they need to be well-characterised so that we can head one off should it ever come our way. And finally, they may provide the raw materials and resources for future missions which can use them as stepping stones to Mars and beyond.

But what makes near Earth asteroids particularly inviting from an engineering point of view is their small velocity relative to Earth. A small delta-V, as rocket scientists call this, means less fuel and more payload. And that translates into longer missions with a better scientific return.

That raises an obvious question: which asteroid do we aim for?

Today, Martin Elvis at the Harvard-Smithsonian Center for Astrophysics in Cambridge and a few buddies examine the possibilities. It turns out that of the 6699 near-Earth asteroids we know, only half a dozen have a delta-V worth considering and are big enough to land on (unless we want to land on an asteroid that is smaller than spacecraft visiting it).

Of course, there are many other near-Earth asteroids that we haven’t discovered, probably an order of magnitude more.

But finding them is particular problem. Their very proximity in an orbit similar to Earth’s means that they spend much of their time on the other side of the Sun and in any case are mainly visible only from Earth’s day-side. That makes them almost impossible to see and track from the ground.

So not only do we have a embarrassing of poverty of choice when it comes to deciding which to visit, there is not much prospect of increasing it in the near future.

And if that weren’t bad enough, human spaceflight is about to come to a sudden end in America. In a few weeks, NASA won’t be able to visit the even International Space Station little more than 200 miles above the surface. And yet it has tentative plans to visit a near Earth Asteroids in 2025 or so.

Last week a new company backed by a number of high-tech billionaires said they would be announcing a new space venture, and there was plenty of speculation of what the company –– called Planetary Resources — would be doing. Many ventured the company would be an asteroid mining outfit, and now, the company has revealed its purpose really is to focus on extracting precious resources such as metals and rare minerals from asteroids.

“This innovative start-up will create a new industry and a new definition of ‘natural resources,’” the group said.

Is this pie in the sky or a solid investment plan?

It turns out this company has been in existence for about three years, working quietly in the background, assembling their plan.

Even though their official press conference isn’t until later today, many of the founders started talking late yesterday. The group will initially focus on developing Earth orbiting telescopes to scan for the best asteroids, and later, create extremely low-cost robotic spacecraft for surveying missions.

A demonstration mission in orbit around Earth is expected to be launched within two years, according to the said company co-founders, and within five to 10 years, they hope to go from selling observation platforms in orbit to prospecting services, then travel to some of the thousands of asteroids that pass relatively close to Earth and extract their raw materials and bring them back to Earth.

But this company also plans to use the water found in asteroids to create orbiting fuel depots, which could be used by NASA and others for robotic and human space missions.

PASADENA, Calif. – Astronomers have discovered what appears to be a large asteroid belt around the star Vega, the second brightest star in northern night skies. The scientists used data from NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory, in which NASA plays an important role.

The discovery of an asteroid belt-like band of debris around Vega makes the star similar to another observed star called Fomalhaut. The data are consistent with both stars having inner, warm belts and outer, cool belts separated by a gap. This architecture is similar to the asteroid and Kuiper belts in our own solar system.

What is maintaining the gap between the warm and cool belts around Vega and Fomalhaut? The results strongly suggest the answer is multiple planets. Our solar system’s asteroid belt, which lies between Mars and Jupiter, is maintained by the gravity of the terrestrial planets and the giant planets, and the outer Kuiper belt is sculpted by the giant planets.

“Our findings echo recent results showing multiple-planet systems are common beyond our sun,” said Kate Su, an astronomer at the Steward Observatory at the University of Arizona, Tucson. Su presented the results Tuesday at the American Astronomical Society meeting in Long Beach, Calif., and is lead author of a paper on the findings accepted for publication in the Astrophysical Journal.

Vega and Fomalhaut are similar in other ways. Both are about twice the mass of our sun and burn a hotter, bluer color in visible light. Both stars are relatively nearby, at about 25 light-years away. The stars are thought to be around 400 million years old, but Vega could be closer to its 600 millionth birthday. Fomalhaut has a single candidate planet orbiting it, Fomalhaut b, which orbits at the inner edge of its cometary belt.

The Herschel and Spitzer telescopes detected infrared light emitted by warm and cold dust in discrete bands around Vega and Fomalhaut, discovering the new asteroid belt around Vega and confirming the existence of the other belts around both stars. Comets and the collisions of rocky chunks replenish the dust in these bands. The inner belts in these systems cannot be seen in visible light because the glare of their stars outshines them.

Both the inner and outer belts contain far more material than our own asteroid and Kuiper belts. The reason is twofold: the star systems are far younger than our own, which has had hundreds of millions more years to clean house, and the systems likely formed from an initially more massive cloud of gas and dust than our solar system.

The gap between the inner and outer debris belts for Vega and Fomalhaut also proportionally corresponds to the distance between our sun’s asteroid and Kuiper belts. This distance works out to a ratio of about 1:10, with the outer belt 10 times farther from its host star than the inner belt. As for the large gap between the two belts, it is likely there are several undetected planets, Jupiter-size or smaller, creating a dust-free zone between the two belts. A good comparison star system is HR 8799, which has four known planets that sweep up the space between two similar disks of debris.

“Overall, the large gap between the warm and the cold belts is a signpost that points to multiple planets likely orbiting around Vega and Fomalhaut,” said Su.

If unseen planets do, in fact, orbit Vega and Fomalhaut, these bodies will not likely stay hidden.

“Upcoming new facilities such as NASA’s James Webb Space Telescope should be able to find the planets,” said paper co-author Karl Stapelfeldt, chief of the Exoplanets and Stellar Astrophysics Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Md.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA’s Herschel Project Office is based at JPL, which contributed mission-enabling technology for two of Herschel’s three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community. More information is online at: http://www.herschel.caltech.edu , http://www.nasa.gov/herschel , and http://www.esa.int/SPECIALS/Herschel/index.html .

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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